What causes transmissions to fail?
#24
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That should help you, Bob.
The one thing that hasn't been mentioned so far is the grip the car is running. A 300wtq miata on star specs is a very different beast than a 300wtq miata on 275 hoosiers on 11's. The latter case is much more likely imo to shatter a gear than the first. The engine is relentless, and the grip is relentless, and the transmission gives up in the middle.
The one thing that hasn't been mentioned so far is the grip the car is running. A 300wtq miata on star specs is a very different beast than a 300wtq miata on 275 hoosiers on 11's. The latter case is much more likely imo to shatter a gear than the first. The engine is relentless, and the grip is relentless, and the transmission gives up in the middle.
#26
That should help you, Bob.
The one thing that hasn't been mentioned so far is the grip the car is running. A 300wtq miata on star specs is a very different beast than a 300wtq miata on 275 hoosiers on 11's. The latter case is much more likely imo to shatter a gear than the first. The engine is relentless, and the grip is relentless, and the transmission gives up in the middle.
The one thing that hasn't been mentioned so far is the grip the car is running. A 300wtq miata on star specs is a very different beast than a 300wtq miata on 275 hoosiers on 11's. The latter case is much more likely imo to shatter a gear than the first. The engine is relentless, and the grip is relentless, and the transmission gives up in the middle.
I have also learned recently after taking a bunch of transmissions apart the NB 5 speed has wider gears throughout than the two versions in the NA particularly noticeable on the input gear. An NB 5 speed is most defiantly going to be a bit stronger than one from an NA. The 6 speeds have much thicker gears than the 5 speed as well but the 5 speed has 3 bearings per shaft instead of 2 which I think might be a design advantage to resist shaft flex. 6 speed was ~12 lbs heavier than the 5 speed Quaife with NB nose, bellhousing and NA tailstock I put together most of that weight I think is in the shafts and gears.
#30
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If you are tracking, I would think yes. There's definitely heat rejection advantages for track. For autocross, I can't recall any threads on this board with instrumented readings of trans temp, but given the relationship of other known cooling mods, autocross heat <<<< track heat.
#31
Bob is breaking trannies because his car is overcoming the physical strength of the gears. The teeth are just not strong enough to hold the power.
A trans cooler will help as long as the engine is not going to be a monster like Bob's. Keeping the fluid at an optimal operating temp is always a good thing. Not only does the cooler keep the fluid cool, but keeps the entire trans colder, helping with any wear/breakage problems related to heat induced fatigue of the gearset and case.
A trans cooler will help as long as the engine is not going to be a monster like Bob's. Keeping the fluid at an optimal operating temp is always a good thing. Not only does the cooler keep the fluid cool, but keeps the entire trans colder, helping with any wear/breakage problems related to heat induced fatigue of the gearset and case.
#33
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IIRC Bob breaks trannies at autocrosses, where tranny temps should be a non-issue. I used to think that a fluid cooler would help improve shaft alignment by keeping the bearings cooler, but I think breaking trannies at an autocross debunks that pretty soundly.
#34
When there's enough power to overwhelm the gearset in short courses like an auto-x where no heat is generated then there's no cooler that will help. But in a lower TQ car (not enough TQ to shear teeth at will), I think a cooler would be beneficial if it is driven hard on track where heat generation will be a factor based on the points I mentioned above.
That being said, I don't personally have a track-dedicated Miata, let alone a small fleet of them, nor do we have any Miata customers at this time. If Andrew or Emilio or any of the other serious track guys are not seeing any benefit from a cooler then that's got to be considered as a hard data point.
That being said, I don't personally have a track-dedicated Miata, let alone a small fleet of them, nor do we have any Miata customers at this time. If Andrew or Emilio or any of the other serious track guys are not seeing any benefit from a cooler then that's got to be considered as a hard data point.
#35
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Bob has also broken them in straight line under load on the track. So not even on hard starts. Last one I read about was 4th sheared off on the back straight of PIR or pacific raceway.
#36
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Yes. I think it's been established that Bob's engine will destroy gearboxes regardless of heat or shock load. He has insane grip and tons of torque.
Some have grenaded gearboxes on the track at considerably lower torque load, no? I would think that a trans cooler could really help a 6-speed live behind, say, 275 wtq instead of Bob's 300+.
Total conjecture, though, as Matthew said.
Some have grenaded gearboxes on the track at considerably lower torque load, no? I would think that a trans cooler could really help a 6-speed live behind, say, 275 wtq instead of Bob's 300+.
Total conjecture, though, as Matthew said.
#37
In current level of grip form a 6 speed has not lasted for more than two days at PIR. 4th gear goes on the back straight out of a corner taken in 4th gear so no shift is involved. I do hold the overall Miata lap record around the track by a good bit however and still holding on to the TT2 lap record. Nobody even got my Pacific raceway lap record even after repaving turn 8 last year helped most people drop about 2 seconds.
#40
Just one.
Broke second gear headed for the finish shoot. I run full boost autocrossing but if I datalog a run I never seem to see full load. Can't load the engine that much in second gear its either accelerating too quickly through the RPM range or spinning the tires. I mainly crank up the manual boost controller cause it seems to build boost quicker at lower rpm when I do and it feels more responsive to throttle inputs. I might be able to do better with electronic boost control but I have never gotten one good enough to be consistant and smooth and repeatable like the manual one. on the track I will see sustained periods of full load through several gears through powerband rev range. Autocrossing is a spastic looking thing by comparison.
Broke second gear headed for the finish shoot. I run full boost autocrossing but if I datalog a run I never seem to see full load. Can't load the engine that much in second gear its either accelerating too quickly through the RPM range or spinning the tires. I mainly crank up the manual boost controller cause it seems to build boost quicker at lower rpm when I do and it feels more responsive to throttle inputs. I might be able to do better with electronic boost control but I have never gotten one good enough to be consistant and smooth and repeatable like the manual one. on the track I will see sustained periods of full load through several gears through powerband rev range. Autocrossing is a spastic looking thing by comparison.
Last edited by bbundy; 02-21-2015 at 11:08 PM.